Projects Under TSC Purview
Proposed minimum criteria to have a project under the TSC purview:
These projects have no active committers. Implicitly having no active committers also means that the project has no objections to be under the TSC purview. In most such cases, the project would likely be archived if it was not put under TSC purview.
The TSC should think that the project is important enough to make it under TSC purview. Instead of specifying specific rules for what is an important project, this should be decided on a case by case basis by a TSC vote.
A project whose all committers are planning to become inactive - can also petition that the project be placed under the TSC purview. The TSC may or may not accept the project to be under TSC purview depending on the TSC vote.
The above should be the minimum criteria. Not all the projects which satisfy the above two criteria should be put under the TSC purview. Whether a particular project should be under the TSC purview, should be decided by a TSC vote.
TSC Purview only means that the TSC members have committer rights on the project and has no other meaning.